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139 lines
6.5 KiB
HTML
139 lines
6.5 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1992-2019 Free Software Foundation, Inc.
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Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
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and David MacKenzie.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled "GNU
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Free Documentation License". -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Structures (STABS)</title>
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<meta name="description" content="Structures (STABS)">
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<meta name="keywords" content="Structures (STABS)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Symbol-Types-Index.html#Symbol-Types-Index" rel="index" title="Symbol Types Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Types.html#Types" rel="up" title="Types">
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<link href="Typedefs.html#Typedefs" rel="next" title="Typedefs">
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<link href="Enumerations.html#Enumerations" rel="prev" title="Enumerations">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Structures"></a>
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<div class="header">
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<p>
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Next: <a href="Typedefs.html#Typedefs" accesskey="n" rel="next">Typedefs</a>, Previous: <a href="Enumerations.html#Enumerations" accesskey="p" rel="prev">Enumerations</a>, Up: <a href="Types.html#Types" accesskey="u" rel="up">Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Structures-1"></a>
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<h3 class="section">5.8 Structures</h3>
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<p>The encoding of structures in stabs can be shown with an example.
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</p>
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<p>The following source code declares a structure tag and defines an
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instance of the structure in global scope. Then a <code>typedef</code> equates the
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structure tag with a new type. Separate stabs are generated for the
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structure tag, the structure <code>typedef</code>, and the structure instance. The
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stabs for the tag and the <code>typedef</code> are emitted when the definitions are
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encountered. Since the structure elements are not initialized, the
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stab and code for the structure variable itself is located at the end
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of the program in the bss section.
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</p>
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<div class="example">
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<pre class="example">struct s_tag {
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int s_int;
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float s_float;
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char s_char_vec[8];
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struct s_tag* s_next;
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} g_an_s;
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typedef struct s_tag s_typedef;
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</pre></div>
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<p>The structure tag has an <code>N_LSYM</code> stab type because, like the
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enumeration, the symbol has file scope. Like the enumeration, the
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symbol descriptor is ‘<samp>T</samp>’, for enumeration, structure, or tag type.
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The type descriptor ‘<samp>s</samp>’ following the ‘<samp>16=</samp>’ of the type
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definition narrows the symbol type to structure.
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</p>
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<p>Following the ‘<samp>s</samp>’ type descriptor is the number of bytes the
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structure occupies, followed by a description of each structure element.
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The structure element descriptions are of the form
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‘<samp><var>name</var>:<var>type</var>, <var>bit offset from the start of the
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struct</var>, <var>number of bits in the element</var></samp>’.
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</p>
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<div class="example">
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<pre class="example"># <span class="roman">128 is N_LSYM</span>
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.stabs "s_tag:T16=s20s_int:1,0,32;s_float:12,32,32;
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s_char_vec:17=ar1;0;7;2,64,64;s_next:18=*16,128,32;;",128,0,0,0
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</pre></div>
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<p>In this example, the first two structure elements are previously defined
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types. For these, the type following the ‘<samp><var>name</var>:</samp>’ part of the
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element description is a simple type reference. The other two structure
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elements are new types. In this case there is a type definition
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embedded after the ‘<samp><var>name</var>:</samp>’. The type definition for the
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array element looks just like a type definition for a stand-alone array.
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The <code>s_next</code> field is a pointer to the same kind of structure that
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the field is an element of. So the definition of structure type 16
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contains a type definition for an element which is a pointer to type 16.
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</p>
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<p>If a field is a static member (this is a C<tt>++</tt> feature in which a single
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variable appears to be a field of every structure of a given type) it
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still starts out with the field name, a colon, and the type, but then
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instead of a comma, bit position, comma, and bit size, there is a colon
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followed by the name of the variable which each such field refers to.
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</p>
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<p>If the structure has methods (a C<tt>++</tt> feature), they follow the non-method
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fields; see <a href="Cplusplus.html#Cplusplus">Cplusplus</a>.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Typedefs.html#Typedefs" accesskey="n" rel="next">Typedefs</a>, Previous: <a href="Enumerations.html#Enumerations" accesskey="p" rel="prev">Enumerations</a>, Up: <a href="Types.html#Types" accesskey="u" rel="up">Types</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Symbol-Types-Index.html#Symbol-Types-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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